Stained mugs / cups . Old lemon juice .
 

I was having a lemsip in my fav mug which was a bit stained and noticed bits of "stain" floating about in it ha ha . So later I found a tub of out of date lemon juice in the cupboard , and poured in half of it into the mug and swished it around, left it an hour and dipped in a dry dishcloth and a few wipes and presto a clean mug again . So don't ever throw out old lemon juice (citric acid , is it ? )

stained teacups
 

Hi,

You can also clean tea stained cups with bread soda, just dampen inside the cup then with a cloth rub round the inside, hey presto, staining gone.

Stained tea cups
 

Salt also works for above, just damp cup rub in salt all round rinse well. Great result.

vinegar
 

good ol vinegar does it too